Inhibition of mitochondrial protein import by mutant huntingtin

Mitochondrial dysfunction has been associated with Huntington's disease. The authors show that mutant huntingtin binds to the mitochondrial import protein TIM23, leading to a deficit in import. Overexpression of TIM23 subunits partially rescued the import defect and subsequent neuronal death. Mitochondrial dysfunction is associated with neuronal loss in Huntington's disease (HD), a neurodegenerative disease caused by an abnormal polyglutamine expansion in huntingtin (Htt). However, the mechanisms linking mutant Htt and mitochondrial dysfunction in HD remain unknown. We identify an interaction between mutant Htt and the TIM23 mitochondrial protein import complex. Remarkably, recombinant mutant Htt directly inhibited mitochondrial protein import in vitro . Furthermore, mitochondria from brain synaptosomes of presymptomatic HD model mice and from mutant Htt-expressing primary neurons exhibited a protein import defect, suggesting that deficient protein import is an early event in HD. The mutant Htt–induced mitochondrial import defect and subsequent neuronal death were attenuated by overexpression of TIM23 complex subunits, demonstrating that deficient mitochondrial protein import causes mutant Htt-induced neuronal death. Collectively, these findings provide evidence for a direct link between mutant Htt, mitochondrial dysfunction and neuronal pathology, with implications for mitochondrial protein import–based therapies in HD.